Electric discharge lamp circuit



' March 16, 1943.

w. OGL ESBEE ELECTRIC DISCHARGE LAMP CIRCUIT Filed Oct. 25, 1941 INVENTOR Wendel! Og/gsbee.

I Patented Mar. 16, 1943 ELECTRIC DISCHARGE LAMP CIRCUIT Wendell Oglesbee, hkewood, Ohio, assignor to Westinghouse Electric Manufacturing. Company, East Pittsburgh, .Pa., a, corporation of Pennsylvania Application October 25, 1941, Serial No. 418,561

My invention relates, generally, to an operating circuit for electric discharge lamps, such as fluorescent lamps, and, more particularly, to a circuit for operating lamps of this character from a constant current series circuit or source where it is desired to maintain the power factor at a relatively high value.

Fluorescent lamps of the conventional type require that around 150 percent of normal operating current be through the flla-' mentary electrodes or cathodes for a short period in order to heat the cathodes prior to applying the starting voltage. 'This is for the purpose of reducing the starting voltage below the abnormally high value for starting the lamp with cold or insufliciently heated cathodes and to increase the life of the lamp. Furthermore, attempting to start the lamp with cold cathodes requires larger and more expensive auxiliary equipment.

Claims. (Cl. 178-124) provide a circuit for operating a fluorescent lamp from a constant current series circuit which shall function to supply the necessary increased starting current for the lamp when connected to the series circuit through an isolating current transformer having such characteristics that its 1 secondary current is so nearly the same under When such lamps are to be operated from a constant current series circuit through isolating.

current transformers or safety coils, which isolates or insulates the lamp from the high voltage of the series circuit and provide the correct operating voltage for the lamp, it has been found that disadvantages result from attempting to use an isolating current transformer having a drooping characteristic with a constant primary current for the purpose of supplying the increased current required for starting. thelamp. These disadvantages result from the fact that the primary power factor of such a transformer is low, being around 60 percent, which results in an increase in the size and cost of the constant current regulator required for the series circuit and also in a lower power factor on the primary feeder supplying this regulator. l

The object of my invention is to provide for overcoming these advantages in a practical and economical manner whereby a fluorescent lamp may be efficiently operated on a constant current series circuit without shortening the normal life of the lamp and without requiring expensive auxiliary control equipment or lowering the power factor of the primary supply circuit. A more specific object of my invention is to provide an operating circuit for a fluorescent lamp supplied with current from a constant cu'r rent series circuit which shall function to supply the necessary increased starting current to the.

lamp and at the same time permit the useof an isolating current transformer having a high primary power factor.

I A more specific object of my invention isto short circuit and normal operating conditions that it will not itself supply the necessary startv ing current for the lamp.

A further object'of my invention is to provide for utilizing auto transformers in the operating circuit of a fluorescent lamp to provide the increased starting current required when the lamp is connected to a constant current series circuit through an isolating current transformer having a high primary power factor and asubstantially constant secondary current.

These and other obiects'of my invention will become more apparent from the following detailed description when read in conjunction with the drawing in which the single figure is a diagrammatic view of a circuit embodying the principal features of my invention.

Referring to the drawing, the reference character ill indicates a well known constant current series circuit supplied with current from a primary feeder circuit, through a constant current regulator (not shown) such as is commonly used for street lighting systems wherein lamps at different points are supplied with current through isolating current transformers or safety coils ll having primary windings I2 and" secondary windings i8.

Such isolating current transformers are well known as they are extensively used in street lighting systems for operating lamps from highvoltage constant current series lighting circuits.

They not onlyfunction as current transformers to operate the lamp connected to the secondary winding thereof, but also as an insulating means to isolate the lamp from the high voltage of the series circuit. Accordingly, they are heavily insulated between the primary and secondary windings and between the windings and case or tank in which the windings are disposed.

As shown, a discharge lamp, such as a fluorescent lamp l4, having cathodes l5 and it is connected to the secondary winding it of one'of the isolating current transformers.

In accordance with the usual practice a thermal starting relay or switch. ll, having a heater It and contact element I9, is utilized to connect the cathodes of the lamp in series circuit relation for a short period of time, usually about closed contact; element and others, such as the Dench type, have a normally open contact element which closes and then opens and remains open.

In order to provide for operating the lamp from the series circuit through an isolating current transformer ll of the high power factor type, a pair of auto-transformers 2| and 22 are utilized to boost the cathode heating current during the starting period.

The windings of these transformers are connected in series across the secondary winding l3 of the isolating current transformer through In View of the foregoing it will be apparent that the operating circuit disclosed makes it possible to operate an electric discharge device, such as a fluorescent lamp, from a constant current-series circuit -or source of supply without attempting to start the lamp with its.cathodes in a cold or insufiiciently heated condition or without resorting to the use of an isolating current, transformer'having a drooping characteristic such as would lower the power factor of the primary circuit feeding the series circuit. This means that a fluorescent lamp or a plurality of such lamps may be efliciently and successfully operated from a constant current series circuit by means of isolating current transformers having such characteristics as will maintain the power factor of the primary supply circuit at'a relatively high value and not require the use of a constant current transformer of excessively large rating.

Although but one embodiment of the invention has been herein shown and described, it is the heater l8 and contact element l9 when the latter is closed. The cathodes l5 and I6 are connected across a portion of the windings of auto-transformers 2| and 22, respectively, so as to receive additional current to that which could be derived from the secondary voltage of the isolating current transformer alone.

When the constant current circuit l becomes energized the 'series heating circuit is closed through the contact element 19 of the thermal switch. This circuit extends from one terminal of the secondary winding l3 thru conductor 24, heater l3, conductor 26, auto-transformer winding 22, conductor 21, contact element l9, 'conductor 28, auto-transformer winding 2i, conductor 29 to the other terminal of the secondary winding I3.

Upon the establishment of this circuit, current not only flows through the windings of the autotransformers 2| and 22 but also through the cathodes l and I6 which are connected across the output terminals of these transformers. Accordingly, it will be apparent that the cathodes will be subjected to a heating current larger' than that which the isolating current transformer ll supplies, due to the boosting of the current supplied by the auto-transformers 2| and 22.

Thus it 'is seen that the auto-transformers function to increase or boost the heating current to a value above the normal operating current which can be supplied by the isolating current transformer.

After a predetermined time delay as determined by the characteristics of the starting switch ll, its contact element [9 opens to interrupt the series heating circuit and effect the discharge of the lamp. When this circuit is open the auto-transformers are rendered ineffective and the lamp circuit operates in the normal manner, the isolating current transformer ll functioning to supply the necessary current to maintain the discharge.

The heater or thermal element l8 of the starting switch I I may be connected in the circuit in any other suitable position such, for example," as in series with either one of the lamp cathodes.

While throughout the descriptionspecific -reference has been made .to auto-transformers for boosting the heating current it is to. be understood that any other suitable device may be used for this purpose.

to be understood that other modifications thereof may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim as my invention:

1. A circuit for operating an electric discharge lamp of the type requiring preheating of they electrodes prior to application of operating voltage from a constant current series supply circuit through an isolating current transformer having insumcient, output current to heat the electrodes to the required temperature during starting comprising, a pair of auto-transformers connected in series to the output terminals of the isolating current transformer, a time-delay starting switch having its contact element interposed in the circuit between the transformers and operable to open said circuit a predetermined time after it is energized, and means for connecting the electrodes of the lamp to the output terminals of said auto-transformers, whereby said transformers supply the additional electrode heating current during starting.

2. The combination with an electric discharge lamp connected to a constant current source through an isolating current transformer and having a time delay starting "switch for interrupting a series heatirig circuit through its'electrodes, of an auto-transformer connected in said series heating circuit in parallel with each electrode for boosting the heating current during the starting period above the amount supplied through the isolating current transformer, thereby to permit the use of an isolating current transformer having a high primary power factor so as to maintain the power factor of the constant current source at a high value.

3. The combination with an isolating current transformer having its primary winding connected in a constant current series supply circuit, of an electric discharge device having electrodes adapted to be preheated prior to the application of operating voltage to the device, a

pair of auto-transformers having their output terminals connected across the electrodes, means connecting one of the primary terminals of each auto-transformer to the terminals of the secondary winding of the isolating current transformer, and means including a, time-delay starting switch connecting the other primary termi nals of the auto-transformers together thereby to provide for boosting the heating current of the electrodes during the starting period of the discharge device as determined by the time that the starting switch is closed.

4. Thecombination with a constant current series supply circuit, of an electric discharge lamp adapted to be energized from said circuit, said lamphaving a pair of electrodes adapted to be preheated prior to the application of operating voltage to the lamp by a heating current exceeding the normal operating current of the lamp, an isolating current transformer having contact element connected so as to interrupt the said connection between the primary terminals a' predetermined time after energization, and means connecting the other terminals of the electrodes to an output terminal of the autotransformers, whereby said auto-transformers function during the starting period of the lamp to increase the starting current flowing in the electrodes above the amount which could be supauto-transformers during the starting period when the control switch is closed.

' 7. A circuit for operating an electric discharge lamp from a constant current source including a current transformer comprising, a pair of auto-transformers having their windings connected inseries circuit relation for connection to the current transformer, a control switch having a contact element connected in said circuit between the transformers operable to open said circuit a predetermined time after energization thereof, and an electric discharge device having a pair of electrodes each of which are connected across the auto-transformers, whereby said auto-transformers function to supply heating current to the electrodes during the time the series circuit is closed by the control switch.

8. In combination, a constant current source of alternating current, an electric discharge device having electrodes and a pair of terminals at each end thereof, a. current transformer having a primary winding connected to the current source and a secondary winding connected to the terminals of the discharge device, a pair of auto-transformers each having one terminal of their windings connected with said one terminal of the electrodes to the secondary winding of the current transformer, means connecting the other terminals of the electrodes to the autotransformer windings, and means including a control switch connecting the other terminals of the auto-transformers together in series cirplied by the isolating current transformer alone.

5. In combination, a constant current source of alternating current supply, a current transformer having. primary and secondary windings, said primary winding being connected to the current source, an electric discharge device having electrodes adapted to be minal of each of said electrodes being connected to the secondary winding of the current transformer, a pair of auto-transformers each having one terminal of-its winding connected to the secondary winding with the .said one terminals of the electrodes, means including a time-delay preheated, one tercontrol switch connecting the other terminals of the windings of the auto-transformers togather, and means-connecting the other terminal of each of the electrodes to an output terminal of the auto-transformers, whereby the voltages of said auto-transformers supplements the current derived from the supply through the current transformer at starting.

6. A circuit for operating electric discharge lamps of the type having electron emitting elecfor heating the electrodes when said control trodes which are preheated from a constant currentse'ries circuit comprising, a high power factor isolating current transformer having a primary winding adapted to be connected in the series circuit and a secondary winding, a pair of auto-transformers having one terminal of each of their windings connected to the secondary winding of the isolating current trainsformer, means including a time-delay control switch connecting the other terminals of the auto-transformer windings together so that said windings are connected in series across the secondary winding of the isolating current transformer, and means connecting the electrode terminals of the discharge device across the auto-transformers, whereby said electrodes are supplied with additional heating current by said cuit relation, said control switch being operable to open the series circuit a'predetermined time afterenergization, whereby during the time the control switch is closed the electrodes are supplied with an additional amount of heating current over that which could be supplied by the connecting current transformer alone.

9. In combination, a constant current series circuit, an isolating current transformer having primary and secondary windings, said primary winding being connected in the series circuit, a discharge devicehaving electron emitting electrodes connected to the secondary winding of the isolating current transformer, a pair of autotransformers having one terminal of each of their windings connected to the secondary winding of the isolating transformer, and their other terminals connected together through a control switch, said electrodes being connected across the auto-transformers, whereby said auto-transformers function to supply additional current switch is closed to start the discharge device.

10. A circuit for operating a discharge device.

having electron emitting electrodes from a constant current series circuit including an isolating current transformer comprising, circuit means including a pair of auto transformers connected in series to the secondary winding of the isolating transformer, means connecting the electrodes of the discharge device across said auto-transformers, and a control switch connected in said series circuit between the autotransformers for interrupting the series circuit a predetermined time after the application of voltage thereto, said auto-transformers functioning to supply additional heating current to the electrodes during the time the control switch is closed to complete the series circuit.

WENDELL' OGLESBEE. 

